The detection of traces of explosive materials is of utmost importance at the present time due to the ongoing risk of terrorism. Detection devices should identify explosives before detonation of the explosive and thus save lives. The technique for detecting such materials should be fast, portable, contact-less, inexpensive, foolproof, and reliable for maximum effectiveness.
A number of methods for detection of explosives have been proposed or are already in service. Non-portable instruments for explosives detection include gas chromatography (involving an electron capture detector), ion mobility spectrometers, mass spectrometers (detecting different masses of ions, separated in a magnetic field after heating the specimen), neutron analysis (based on neutron excitation of atoms in explosives), nuclear quadrupole resonance, and x-ray detection. Optical techniques include transmission measurements of explosives contained in solutions, or in the gaseous state in the ultraviolet, visible, or infrared range, fluorescence spectroscopy (coupled with immunoassay reactions whereby the explosive fluoresces when in contact with a sensor), quenching of photoluminescence (of an appropriate inert material by an explosive vapor), and photofragmentation (by separating NO2 into O and NO by a laser followed by detection of NO using laser-induced fluorescence). Among the portable detectors are calorimetric detection devices (involving for example alkali-based chemicals which change color when they are exposed to certain types of explosives). A dog trained to detect explosive vapors can also be effective.
Although several methods are available for detecting explosives, a new, relatively simple, real-time, portable, high sensitivity and particularly, a stand-off technique that requires little or no sample preparation is needed.